package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        simpleExecutor simpleExecutor = new simpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap()
                .get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    /**
     * 插入一条记录
     *
     * @param mappedStatementId
     * @param params
     * @return
     * @throws Exception
     */
    @Override
    public int insertOne(String mappedStatementId, Object... params) throws Exception {
        simpleExecutor simpleExecutor = new simpleExecutor();
        return simpleExecutor.update(
                configuration, configuration.getMappedStatementMap().get(mappedStatementId), params);
    }

    /**
     * 删除一条记录
     *
     * @param mappedStatementId
     * @param params
     * @return
     * @throws Exception
     */
    @Override
    public int delete(String mappedStatementId, Object... params) throws Exception {
        simpleExecutor simpleExecutor = new simpleExecutor();
        return simpleExecutor.update(
                configuration, configuration.getMappedStatementMap().get(mappedStatementId), params);
    }

    /**
     * 根据主键更新记录
     *
     * @param mappedStatementId
     * @param params
     * @return
     * @throws Exception
     */
    @Override
    public int updateById(String mappedStatementId, Object... params) throws Exception {
        simpleExecutor simpleExecutor = new simpleExecutor();
        return simpleExecutor.update(configuration, configuration.getMappedStatementMap().get(mappedStatementId), params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(
                DefaultSqlSession.class.getClassLoader(), new Class[] {mapperClass}, new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                        // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                        // 方法名：findAll
                        String methodName = method.getName();
                        String className = method.getDeclaringClass().getName();

                        String statementId = className + "." + methodName;
                        if (configuration.getMappedStatementMap().get(statementId).getSql().startsWith("insert")) {
                            return insertOne(statementId, args);
                        } else if (configuration.getMappedStatementMap().get(statementId).getSql().startsWith("delete")) {
                            return delete(statementId, args);
                        } else if (configuration.getMappedStatementMap().get(statementId).getSql().startsWith("update")) {
                            return updateById(statementId, args);
                        }

                        // 准备参数2：params:args
                        // 获取被调用方法的返回值类型
                        Type genericReturnType = method.getGenericReturnType();
                        // 判断是否进行了 泛型类型参数化
                        if (genericReturnType instanceof ParameterizedType) {
                            List<Object> objects = selectList(statementId, args);
                            return objects;
                        }
                        return selectOne(statementId, args);
                    }
                });
        return (T) proxyInstance;
    }
}
